a MODERNIZATION
ELEVATOR
GUIDELINES
FOR
EMERGENCY
GENERATORS
by Patrick J. Welch
a
Indicates an Online Feature
ers must be upgraded to operate with an adjustable-speed
elevator solid-state drive. Each test conducted followed
ASME A17.1 requirements.
After establishing a benchmark on utility power, the generator was started, and a power
loss was mimicked at the transfer switch. While on emergency
power, the quality of power was
measured as defined here:
◆ frequency;
◆ total harmonic distortion
(THD) for current and RMS
voltage;
◆ RMS voltage; and
◆ current.
After
comparing
utility
power quality to the emergency
generator power, the quality of
power with no load was determined. The load on the elevator
was then increased until 125%
of rated capacity was reached,
as required by A17.1. Continued .
▲
Passengers trapped in elevators need every opportunity
to escape an emergency situation. If designed to operate on
standby power, the emergency generator must operate elevators safely and reliably. If the elevators do not operate
properly while on emergency power, serious consequences can occur.
The most commonly ignored operation of
an elevator is its ability to operate properly
on standby power. The American Society of
Mechanical Engineers (ASME) A17.1 and
most local codes require elevator standby
power testing annually, with no-load and
full-load (125% of capacity) test every five
years. Furthermore, if more than one elevator is capable of running simultaneously,
they shall be tested simultaneously.
Experience shows that many buildings
ignore this code requirement. Some large facilities, including hospitals, have not tested
any of the elevators on emergency power in
over 20 years! With the advent of SCR and
VFAC drives for elevators and other devices,
existing emergency generators are often not
capable of providing the proper power to operate the elevators in an emergency.
Keep in mind that older elevator systems often do not operate at the original
contract speed. Therefore, if any equipment has been added
since the original installation, the change to a solid-state
drive operating at the proper speed can cause unpredictable
problems. Additionally, older emergency generators have a
difficult time with the rapid changes in current demand that
solid-state drives require.
Current and voltage harmonics also differ greatly from
utility power to the emergency generator power supply.
Improper grounding methods and increased impedance
of the generator system can cause additional problems
with sensitive devices on the emergency bus, due to increased harmonics and RFI.
Several tests with the Reliable Power Meter® monitor
have determined that existing generator or emergency feed-
March 1998 ◆ Elevator World 45
ELEVATOR GUIDELINES
Continued
The most common problems operating on emergency
power discovered to date have been:
1. Increase in THD, up to a 300% increase over utility power;
2. Improper or inadequate grounding methods;
3. Poor voltage regulation (>25%); and
4. Voltage sags in excess of solid-state drive parameters.
Since our testing program was started in February 1997,
roughly one Syska & Hennessy existing building project
per month has required significant upgrading of the emergency generator and/or emergency feeder, if a modern
solid-state elevator drive is desired. Often, the client is
unprepared for the additional expense of upgrading the
emergency generator, and motor generator elevator drives
have to be specified to save the client the emergency generator upgrade costs, as well as the potential disaster of
a failed emergency system.
To help prevent problems, a conservative course of
action developed through research, testing and feedback
from knowledgeable clients and vendors is recommended.
This does not mean that you cannot specify outside the
suggested parameters. It does mean, however, that you
must be careful and should thoroughly investigate existing
conditions to predict the effect of all of the various types
of drives on the emergency generator.
Other potential problems of concern include:
1. What other devices are operating on that emergency bus? UPS systems? VFD for fire pumps?
2. Are other harmonic-rich devices on the same bus?
For example, electronic ballast light fixtures – the harmonics
of which can create problems for elevators.
3. Are harmonic-sensitive devices – such as radio or
telephone dispatching equipment or critical computer
equipment – on the same emergency bus?
4. Can the emergency generator handle the chopped
waveform of regenerative power from the elevator SCR
without affecting its performance?
5. Is the voltage regulator for the emergency generator
designed for the worst-case scenario, as the code requires?
Keep in mind that several different types of elevator
drives are in use today, including:
◆ Six-pulse SCR drives (typically filtered to 5% THD);
◆ 12-pulse SCR drive (no filter);
◆ Variable frequency/variable voltage AC (nonregenerative);
◆ Variable frequency/variable voltage AC (regenerative)
– rare but increasingly more common;
◆ Motor generator set; and
◆ Across the line and WYE delta (hydraulic and rack
& pinion).
It is recommend that the emergency generator specifications be coordinated with the exact elevator drive to be
used on the project.
Hydraulic Elevators
It is recommended that hydraulic elevators not be put
on the emergency generator unless they are critical hospital patient care elevators that will need to be used
throughout the power outage. It is far more efficient to
provide an emergency-battery lowering device on these
elevators to rescue the passengers instead of including a
large horsepower motor on the emergency generator just
to allow passengers one trip to get out of the elevator.
46 March 1998 ◆ Elevator World
Sizing Emergency Generators
Do not design more than two elevators equipped with
solid-state drives to run on the same emergency bus simultaneously. Research and field testing reveals that the harmonics and regenerative nature of most elevator drives can
cause voltage distortion problems on the same bus. Do not
allow adjustable-speed solid-state drives of any type to exceed 50% of the capacity of the emergency generator. This
includes other solid-state drives in the building that will be
using the same emergency power supply.
Should circumstances require a greater than 50%
drive capacity of the emergency generator, ensure that
the generator manufacturer is aware of the type and
quantity of the drives. Serious consideration should be
given to specifying the allowable voltage distortion. If
there is an overall voltage distortion limit, make sure that
the generator unloaded waveform is well below that
limit. It is virtually impossible to filter an inherently distorted generator waveform.
Existing Buildings
Check the governor/regulator of the emergency generator; older buildings being renovated often have mechanical governors on the emergency generators. Modern solid-state drives simply cannot operate properly
with the voltage distortion created by a solid-state drive
Phase C RMS Voltage Aug 15, 1997 10:20:57
300
270
240
220
200
10:00
August 15, 1997
Figure 1: Utility power during full load runs of elevator;
Voltage fluctuation is less than 6 volts.
Phase C RMS Voltage Aug 15, 1997 11:04:44
300
270
240
220
200
11:21
August 15, 1997
Figure 2: This is the same elevator on emergency power.
The voltage fluctuation is up to 40 volts.
and an emergency generator with a mechanical governor. Keep in mind that elevator drives move people, not
fans or computers, and the operating tolerances are
tight. Simply put, rarely is it recommended to allow an
elevator with a solid-state drive to operate on an emergency generator without a solid-state regulator being installed on the emergency generator.
For example, Figures 1 and 2 show a graphic expression of the quality of the voltage of an elevator system
with a motor generator drive while on utility power during
a full-load weight test of the elevators. Had solid-state
drives been utilized, the emergency generator or elevator
would not have operated properly.
Testing
All existing buildings should be properly tested to determine a final design. The test should not use a load bank.
It is critical to determine what other sensitive devices operate
on the emergency generator. The load bank is simply too
clean (no reactance or interference) to properly determine
how the elevator affects the system.
Elevator maintenance contracts should define this requirement clearly. Experience shows that if the building
does not require this test, the elevator maintenance contractor will consider it a building manager's responsibility.
The load bank is also too clean to determine if the
elevator drive will affect other devices on the same emergency generator bus - items such as electronic ballast
lights, fire control systems, radio dispatching centers and
other communication devices.
A "blackout" type test is recommended whenever possible, so all concerned parties will understand which device operates properly and which devices have difficulties
under emergency conditions. In other words, all devices
designed to operate on the emergency generator should
be tested simultaneously. This will allow building management to understand how all of the life/safety devices
will operate on emergency power while in full control of
the power source.
It is far better to fail this controlled blackout test due
to an improper design or modification under controlled
circumstances than to discover that the elevators either
fail to operate or, even worse, cause the emergency generator to trip out, causing other life/safety devices to fail
during a true emergency. Updated one-line diagrams for
all life/safety systems should also be reviewed and updated during these tests.
Elevators are part of an entire building operation system. Elevator drives affect the building's electrical system
and, in turn, are affected by the building's electrical devices
as well. Close coordination of drives and distribution of
power is critical to a building's safe and reliable operation.
Patrick J. Welch is President of Vertical Transportation Excellence, a
division of Gannett Fleming, Inc. He oversees their Vertical
Transportation offices located in Washington, Baltimore,
Philadelphia, New York and Connecticut. In addition, he is a
member of the A17 Escalator and Moving Walk Committee and
chairs the "Vertical Transportation Chapter 12 in the Institute of
Electrical and Electronics Engineers, Inc. (IEEE) Std. 241,
Recommended Practice for Electrical Systems in Commercial
Buildings."
March 1998
Elevator World 4 7